The Value of a Forage Analysis
Forage makes up the major portion of livestock diets. A livestock producer maximizes the value of a forage when the diet is properly balanced considering the nutritional value of the forage. A forage sample needs to be analyzed for moisture, protein fiber, (ADF and NDF which allows us to calculate TDN or net Energy) and minerals. An analysis of a forage is the only positive means of knowing the nutrient content. Book values or guesses can be very misleading in balancing a ration. Underestimating the protein content of alfalfa hay by 2% in a diet fed to dairy cows at 25 lbs./ day could result in the excess feeding of 100 lbs. soybean meal/day to a 100 cow herd.
Hay Test Requirements
- Forage sample is fully dried in an oven to determine the % water. Hay will usually have 7-20% moisture.
- A calculated value based on N x 6.25. Made up of true protein and non protein nitrogen. Early cut, leafy forages are highest in crude protein.
Acid Detergent Fiber:
- ADF is the % of the highly indigestible portion of the plant. The lower the ADF value , the higher the digestibility and energy value of a hay.
Neutral Detergent Fiber:
- NDF is the % of the cell wall of a plant. Directly related to fill or intake. The lower the NDF, more the animal can eat.
Relative Feed Value:
- RFV is an over all indicator of forage quality Calculated from ADF and NDF. Comparing alfalfa, a RFV of 100 equals full bloom mature alfalfa. Grasses at similar stages of maturity will have a lower RFV because of a higher %NDF.
|Alfalfa, Alfalfa/Mix||Grass Hay|
| Relative Feed Value || Acid Detergent Fiber || Crude Protein |
| RFV || ADF || CP percent |
|Supreme|| Over 180 || Under 27 || --------- |
|Premium|| 150-180 || 27-30 || Over 13 |
|Good|| 125-150 || 30-32 || 9-13 |
|Fair|| 100-125 || 32-35 || 5-9 |
|Low|| Under 100 || Over 35 || Under 5 |
Quantitative factors are approximate, and many factors can affect feeding value. Based upon 100 percent dry matter. RFV calculated value based upon American Forage and Grasslands Council formula. End usage may influence hay price or value more than test results.